A plasma processing apparatus includes an accommodation chamber accommodating a wafer serving as a substrate. The plasma processing apparatus generates a plasma from a processing gas introduced into the accommodation chamber and performs a desired plasma process on the wafer by using the plasma. When the plasma process is a dry etching process, reaction products are produced from the reaction between the plasma and an etched material. The reaction products are deposited as deposits on the surface of a constituent part of the accommodation chamber.
On the other hand, a sheath 71 is generated along a surface 70 of a constituent part exposed to the plasma in the accommodation chamber, and ions 72 in the plasma are implanted toward the surface of the constituent part by the sheath 71 (see FIG. 7A). The implanted ions 72 sputter the deposits deposited on the surface of the constituent part to remove the deposits from the surface of the constituent part. Generally, the amount of the deposits deposited on the surface of the constituent part is equal to or less than the amount of the deposits removed by ion sputtering, so that the deposits are rarely deposited.
In recent years, precise control over the distribution of a plasma, particularly, the density of electrons in the accommodation chamber has been required to achieve uniformity in the plasma process performed on the wafer. Correspondingly, the provision of a protrusion, a groove, or a step at an upper electrode facing the wafer has been proposed (see, e.g., Patent Document 1).
[Patent Document 1] Japanese Patent Application Publication No. 2009-239014
As shown in FIG. 7B, a bent sheath 74 is generated at a protrusion or a groove having a corner 73 of an approximately right angle. However, ions 75 are created approximately perpendicularly to the sheath 74, and therefore, the ions 75 are created from the bent sheath 74 in a diffused manner. As a result, the number of ions 75 implanted into the corner 73 per unit area is much less than in the other regions, and the amount of deposits removed by ion sputtering is reduced. Accordingly, deposits 76 may be deposited at the corner 73 and in the vicinity thereof. The deposited deposits 76 are peeled off into particles, which are attached to a wafer to cause wafer defects.